Nuclear bone scan demonstrates focal uptake in the L3 vertebral body and posterior elements. Minimal uptake in the S1 vertebral body. Diffuse uptake in the left 5th rib and probably involving the adjacent T5 vertebral body. Geographic uptake in the frontal skull and skull base. Uptake in single mid cervicle vertebral body and posterior elements. Focal uptake in the posterior right calcaneous.

Diagnosis: Pagets Disease

Discussion:

Paget disease

Epidemiology

Likely viral etiology with increasing incidence with aging. 3-4% over 40 years old and 10-11% over 80 years old. Slight male predominence. Pagets disease usually affects the axial skeleton to include most commonly pelvis, spine and skull. The femurs are also often affected. Less often shoulders, forearm, ribs, fibula, hands and feet. Polyostotic disease is prominant with tendency to be right sided.

Three phases

Lytic phase occurs early with osteoclastic activity the greatest. Mixed phase is mix of osteoblastic and osteoclastic activity. In this phase trabecular and cortical thickening with enlargement of the bone can be seen. Blastic phase which occurs later with osteoblastic activity predominate.

Clinically

Symptoms include local pain, tenderness and increased warmth. Bone bone enlargement can also be seen which can cause neuromuscular symptoms. Patients may also suffer from bowing deformities, decreased range of motion and kyphosis. Complications most commonly occur from osseous weaking with fractures and bone deformity as well as secondary osteoarthritis from altered biomechanics.

Imaging

Imaging findings depend on the predominant phase of the disease. In the lytic phase, well-defined osteolytic lesions can be seen in the skull, known as osteolysis circumscripta. Lytic lesions in the long bones have more wedge shape with sharp lucent leading edge. This can be seen in both radiographs and CT. CT can help to demonstrate lack of cortical destruction or soft tissue mass.

Mixed phase demonstrates coarsening and thickening of trabecular pattern and cortex along lines of stress as well as disorganized areas. In the spine, cortical thickening can result in picture frame appearance of the vertebral body.

In the blastic phase areas of previous trabecular and cortical thickening can be obscured by extensive sclerosis, such as seen with "ivory vertebral body". Bone enlargement can also be seen in this phase. In the skull, scattered areas of focal sclerosis "cotton wool" can also be seen.

MRI appearance of trabelcular and cortical thickening shows low signal on all pulse sequences. The marrow signal is more dependendent on phase. Usually the yellow marrow signal is maintained especially in the mixed phase. Heterogenous bone marrow T1 and T2 signal can be seen in lytic or early mixed active phase especially in water sensitive images. The last appearance is seen in late blastic phase with low signal throughout the marrow secondary to the sclerosis seen in this stage. Secondary to Paget's hypervascularity, enhancement may be seen especially in more active disease.

Nuclear medicine can show extent/polyostotic nature of Paget Disease with increased radiopharmaceutical uptake in all three phases. Very late disease, however may demonstrate normal appearance on bone scan with continued abnormality on radiographs. Amount of radiopharmaceutical to a specific area depends on blood flow and the amount of new bone formation. Because of its hypervascular nature, Paget disease can be detected scintigraphically before lucency visualized radiographically.

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